August 2023 - 29

GRAPES
time the brown " scorched " leaves indicate the pest has
been in the area, the plant has already been infected for
a year.
" So we've got vines that are infected in the summer,
asymptomatic in the fall, sitting with the disease all
winter and carrying the disease the next summer when
sharphshooters are spreading it to new vines, " Haviland
said. " Then after that's already occurred, we can see the
symptoms and pull (vines) out. "
Citrus trees are popular GWSS hosts but they and
the fruit aren't affected. It's not uncommon, however,
for citrus and grape crops to be in the same area in
California. GWSS adults, which are large for leafhoppers,
are highly mobile and often move between adjacent
orchards and vineyards throughout the day.
" You treat one orchard, they'll fly to a vineyard and then
fly back later, " Haviland said. " It takes a huge industry
coordination. In some areas, all of them (growers) treat
at the same time. Once the movement to grapes start,
typically all growers are applying neonicotinoids for vine
mealybugs as well as glassy-winged sharpshooters and
leafhoppers, so it's three birds with one stone. "
That cooperation between growers, as well as
homeowners who let agents from the state spray trees
and vines in their yards, is one part of California's push to
control GWSS/Pierce's disease. Government programs
that pay for citrus spraying (because GWSS don't kill
citrus, there's no incentive for growers to treat their
groves), traps, surveys and Pierce's disease tracking are
also necessary.
Although a California program releases parasitoid
wasps that attack GWSS eggs, the sharpshooters are hard
to propagate to supply eggs for a breeding program, and
those programs are focused more on urban areas and
not commercial production areas. Because there aren't
pheromones available to attract the GWSS, sticky traps
(the ubiquitous yellow cards) are useful in detecting their
presence, but not as a means to control the population.
The traps should be placed in quarter-mile grids to
chart the pest's movement, Haviland said.
Haviland encourages Washington growers to be vigilant
for signs of Pierce's disease and rely on experts with UC's
Cooperative Extension and California Department of Food
and Agriculture programs for information.
" We are never going to get rid of Xylella and we're never
going to get rid of these sharpshooters where they are
established, " he said. " The exceptions are in satellite
areas, urban areas. Yes, we have had lots of successful
eradications, but once it's in commercial (production)
areas, that's not going to happen. "
Premium, Trusted
High-Load Copper
The same trusted copper you can rely on
in a convenient low-dust formulation that
destroys disease-causing pathogens for
optimal prevention and control to fight a
variety of diseases across specialty crops.
Now with an improved formulation for
better mixing and handling.
CERTISBIO.COM | 1-800-250-5024
©2023 Certis USA
FRUITGROWERSNEWS.COM | 29
http://www.CERTISBIO.COM http://www.FRUITGROWERSNEWS.COM
August 2023

Table of Contents for the Digital Edition of August 2023
